Spread spectrum receiver with multi-bit correlator

Abstract

A system and a method to track GPS (Global Positioning System) satellite signal in a GPS receiver that includes an expanded capture window to rapidly reacquire the satellite signal after the satellite signal has been obstructed or when there is other type of signal loss. The expanded capture window includes a plurality of additional early and late correlations for maintaining synchronization of the GPS signal with a generated replica signal when positional error has accumulated during the time of the signal loss. The plurality of additional early and late correlations may be delayed from each other by a multiple of a fraction of a chip and may be performed in one or multiple channels of the GPS receiver. The adjoining code samples in the replica signal may also be offset by a fraction of a chip or by a multiple of the fraction of a chip.

1. A method for global positioning system (GPS) navigation, the method comprising:
 tracking at least one GPS signal from a GPS satellite, including performing a series of early correlation, a series of prompt correlations, and a series of late correlations to define a capture window for maintaining synchronization of the at least one GPS signal with a generated replica signal; and 
 reacquiring the at least one GPS signal, including performing a plurality of additional early correlations and a plurality of additional late correlations so as to create an expanded capture window for maintaining the synchronization. 
 
   
   
     2. The method of  claim 1  wherein performing the plurality of additional early correlations and the plurality of additional late correlations comprises:
 generating a plurality of code samples that are correlated with the at least one GPS signal; and 
 delaying each of the plurality of code samples by a multiple of a fraction of a chip to generate a plurality of early code samples, and a plurality of late code samples, wherein adjoining code samples are offset by the fraction of a chip. 
 
   
   
     3. The method of  claim 1  wherein performing the plurality of additional early correlations and the plurality of additional late correlations comprises:
 generating a plurality of code samples that are correlated with the at least one GPS signal; and 
 delaying each of the plurality of code samples by a multiple of a fraction of a chip to generate a plurality of early code samples, and a plurality of late code samples, wherein adjoining code samples are offset by a multiple of the fraction of a chip. 
 
   
   
     4. The method of  claim 2  wherein the fraction of a chip comprises less than one-half chip. 
   
   
     5. The method of  claim 3  wherein the fraction of a chip comprises less than one-half chip. 
   
   
     6. The method of  claim 1 , wherein the plurality of additional early correlations and the plurality of additional late correlations are performed in one channel of a GPS receiver. 
   
   
     7. The method of  claim 1 , wherein the plurality of additional early correlations and the plurality of additional late correlations are performed in more than one channel of a GPS receiver. 
   
   
     8. The method of  claim 1 , wherein the plurality of additional early correlations and the plurality of additional late correlations are performed in more than one channel of a GPS receiver, wherein additional channels of the GPS receiver are concurrently used to track the at least one GPS signal. 
   
   
     9. An apparatus for global positioning system (GPS) navigation, the apparatus comprising:
 a satellite receiver configured to receive GPS satellite signals; 
 a plurality of satellite tracking channels coupled to the satellite receiver, wherein each of the plurality of satellite tracking channels is configured to, 
 track at least one GPS signal from a GPS satellite, including performing a series of early correlation, a series of prompt correlations, and a series of late correlations to define a capture window for maintaining synchronization of the at least one GPS signal with a generated replica signal; and 
 reacquire the at least one GPS signal, including performing a plurality of additional early correlations and a plurality of additional late correlations so as to create an expanded capture window for maintaining the synchronization; and 
 a satellite processor coupled to receive outputs from the plurality of satellite tracking channels. 
 
   
   
     10. The apparatus of  claim 9  wherein each of the plurality of satellite tracking channels is configured to:
 generate a plurality of code samples that are correlated with the at least one GPS signal; and 
 delay each of the plurality of code samples by a multiple of a fraction of a chip to generate a plurality of early code samples, and a plurality of late code samples, wherein adjoining code samples are offset by the fraction of a chip. 
 
   
   
     11. The method of  claim 9  wherein each of the plurality of satellite tracking channels is configured to:
 generate a plurality of code samples that are correlated with the at least one GPS signal; and 
 delay each of the plurality of code samples by a multiple of a fraction of a chip to generate a plurality of early code samples, and a plurality of late code samples, wherein adjoining code samples are offset by a multiple of the fraction of a chip. 
 
   
   
     12. The method of  claim 10  wherein the fraction of a chip comprises less than one-half chip. 
   
   
     13. The method of  claim 11  wherein the fraction of a chip comprises less than one-half chip. 
   
   
     14. The method of  claim 9 , wherein the plurality of additional early correlations and the plurality of additional late correlations are performed in one channel of the satellite tracking channels. 
   
   
     15. The method of  claim 9 , wherein the plurality of additional early correlations and the plurality of additional late correlations are performed in more than one channel of the satellite tracking channels. 
   
   
     16. The method of  claim 9 , wherein the plurality of additional early correlations and the plurality of additional late correlations are performed in more than one channel of the satellite tracking channels, wherein additional channels of the satellite tracking channels are concurrently used to track the at least one GPS signal. 
   
   
     17. A computer readable medium having instructions stored thereon, which when executed control a global positioning system (GPS) navigation system, wherein controlling includes:
 tracking at least one GPS signal from a GPS satellite, including performing a series of early correlation, a series of prompt correlations, and a series of late correlations to define a capture window for maintaining synchronization of the at least one GPS signal with a generated replica signal; and 
 reacquiring the at least one GPS signal, including performing a plurality of additional early correlations and a plurality of additional late correlations so as to create an expanded capture window for maintaining the synchronization. 
 
   
   
     18. The method of  claim 17  wherein performing the plurality of additional early correlations and the plurality of additional late correlations comprises:
 generating a plurality of code samples that are correlated with the at least one GPS signal; and 
 delaying each of the plurality of code samples by a multiple of a fraction of a chip to generate a plurality of early code samples, and a plurality of late code samples, wherein adjoining code samples are offset by the fraction of a chip. 
 
   
   
     19. The method of  claim 17  wherein performing the plurality of additional early correlations and the plurality of additional late correlations comprises:
 generating a plurality of code samples that are correlated with the at least one GPS signal; and 
 delaying each of the plurality of code samples by a multiple of a fraction of a chip to generate a plurality of early code samples, and a plurality of late code samples, wherein adjoining code samples are offset by a multiple of the fraction of a chip. 
 
   
   
     20. The method of  claim 18  wherein the fraction of a chip comprises less than one-half chip. 
   
   
     21. The method of  claim 19  wherein the fraction of a chip comprises less than one-half chip. 
   
   
     22. The method of  claim 17 , wherein the plurality of additional early correlations and the plurality of additional late correlations are performed in one channel of a GPS receiver. 
   
   
     23. The method of  claim 17 , wherein the plurality of additional early correlations and the plurality of additional late correlations are performed in more than one channel of a GPS receiver. 
   
   
     24. The method of  claim 17 , wherein the plurality of additional early correlations and the plurality of additional late correlations are performed in more than one channel of a GPS receiver, wherein additional channels of the UPS receiver are concurrently used to track the at least one GPS signal.